Studies Concerning the Mechanism Controlling the Initiation of Lactation at Parturition Iii. Can Estrogen Account for the Precipitous Increase in the Lactogen Content of the Pituitary Following Parturition?¹,²

THE FOLLOWING FACTS have been established concerning the relation of the lactOgenic hormone to the initiation of lactation, a). Estrogen can increase the secretion of lactogenic hormone by the pituitary and initiate lactation, b). During pregnancy there is little if any increase in lactogenic hormone despite the presence of large amounts of estrogen. This is attributed to the predominant quantity of progesterone which overrides certain effects of estrogen during pregnancy. Evidence will now be submitted showing that the diminution or cessation of progesterone secretion just prior to parturition permits estrogen to assume the ascendency and quickly stimulate an increased elaboration of lactogenic hormone, which in turn brings about the onset of lactation. There is considerable evidence in favor of the view that estrogen plays a major rô1e in the initiation of labor, and it is not unexpected that this event should be closely associated with the initiation of milk secretion.